1. Field of the Invention
The present invention relates to an improved material formulation for intravascular catheters, which may be used to extrude the body of a catheter or conduit to be introduced into a body, such as interventional guiding catheters, coronary catheters, drainage catheters, chemotherapy delivery catheters, radiology catheters or neuroradiology catheters, as well as the insulation or protective cover of electrical conduits, such as temporary leads for electrically stimulating the heart or other organs. The material formulation may also be used to provide conduits for surgical instruments used in keyhole operations such as cholisystectomy and laparoscopic tubal ligation, or for biopsy forceps.
2. Description of the Prior Art
Catheters are thin, flexible tubes, which are introduced into a vessel, such as a vein or artery, and guided to select sites, usually, but not exclusively, within the vascular system. In the case of an angiographic catheter, contrast media is injected into a vessel through the catheter""s lumen to visualize the vessel""s structure and anatomic changes within the vicinity of the distal opening of the catheter, for the purpose to diagnose disease and determine the direction, distribution and rate of flow.
Cardiac catheterization was first performed (and so named) by Claude Bernard in 1844. The subject was a horse, and both, the right and left heart ventricles were entered by a retrograde approach from the jugular vein and carotid artery. See Counard, Andre û Nobel Lecture, Dec. 11, 1956, Elsevier Pub. Co., 1964 p. 529.
In 1929, Werner Forssmann was credited with being the first person to a pass a catheter into the heart of a living person, himself. See Forssman W: Die Sondierung des rechten Herzens. Klin. Wochenschr. 8: 2085,1929.
Catheters are designed and manufactured using biocompatible polymer materials, which are compounded with certain radiopaque salts, known as radiopaque media, to visualize or register the catheter within the human body using fluoroscopy or conventional X-ray imaging recorded on film or magnetic media. The blending of the radiopaque medium demands that the polymer (typically a thermoplastic compound) be molten and the radiopaque medium be uniformly mixed with the viscous polymer. This compounding procedure subjects the commonly used radiopaque media, such as bismuth subcarbonate, to temperatures close to their thermal decomposition, which in turn may initiate the breakdown of the compound""s physical properties. Bismuth subcarbonate is a white powdery salt that will thermally decompose into yellow bismuth trioxide during a typical compounding temperature excursion. This is further aggravated during the extrusion of the catheter body when additional heating is experienced by both, the bismuth subcarbonate and the polymeric compound. Further thermal exposure of the extruded catheter during the manufacturing process will continue to cause the bismuth subcarbonate and polymer compound to deteriorate.
Other commonly used radiopaque media, such as barium sulfate (BaS04), are also known to break down during high temperature compounding. Advances in both diagnostic and interventional catheterization procedures require a higher level of product performance than in the past. These improvements in catheter design include as wire braiding, high performance plastics, etc. Despite the problems caused by heat exposure, the use of thermally stable radiopaque media to reinforce the catheter appears desirable, as it does improve the polymer compound and the subsequently extruded catheter body with longer than earlier expected shelf life.
The ideal material for a catheter body, in addition to its excellent bio- or hemocompatibility, is expected to have high strength, high pressure rating, high flow rate due to low hydraulic resistance, chemical and thermal stability over its long shelf life, radiopacity when the application demands it, and excellent torque transmission characteristics along its length, especially for angiographic applications. In addition, it should be possible to extrude the material into various shapes, resulting in thin and uniform walls, smooth lumina, and the extruded surface should be suitable for bonding to the other components of the catheter product.
A catheter coated with zirconium oxide is disclosed in U.S. Pat. No. 5,647,858.
The use of ceramics to reinforce certain composite structures is known. Ceramics are used as insulators in spark plugs due to their thermal stability and high mechanical and dielectric strength. Ceramics are also known to be extremely inert and biocompatible, certain ceramics are used in implantable prosthetic devices such as the ball of an artificial femur in a hip joint. The present invention utilizes a fine ceramic powder known as monoclinic zirconia (zirconium dioxide, ZrO2) as an ambifunctional radiopaque medium that may provide the required radiopacity and reinforce the polymeric compound for intravascular catheters.